A large number of coils, each thereof generally called a magnet wire, formed by winding an insulated electric wire, have thus far been used in a variety of electrical equipment. Those coils are for various applications including use in a transformer for generating a high voltage. For the generation of a high voltage, the number of windings on the secondary winding side of a transformer is increased. If a high potential difference occurs between adjacent insulated electric wires within the secondary wiring, the potential difference will exceed a dielectric breakdown voltage to thereby cause short circuiting, the so-called rare short, thereby damaging the equipment.
In order to avoid such an event, a winding frame 500 was partitioned into a number of parts with an insulator interposed therebetween in the past such that sidewalls 510, and intermediate walls 520 are provided by stages, increasing the number of the intermediate walls 520 according to an application voltage, as shown in FIG. 13, thereby applying partial winding to the winding frame 500 with an insulated electric wire 540. However, since the winding frame 500 was separated by the insulator, it was difficult to achieve reduction in size, resulting in a high cost. That is, the coil became larger in volume, and was unsuitable for equipment of which miniaturization is required. Furthermore, for use in a HID (High Intensity Discharge Lamp), the demand for which is increasing because it is high in directivity and is capable of brightly and clearly illuminating a target away at a distance, the coil needs to have a large conductor cross sectional area since a high voltage temporarily occurs upon the lighting of a HID, and a large current flows after the lighting while miniaturization is required, so that a flat type electric wire has been often used. The flat-type electric wire, however, has had problems of a high cost and poor workability.
Further, in order to use a coil as the voice coil of a speaker, there is the need for holding back the inductance to thereby cause a large current to flow through a narrow space, so that the flat-type electric wire is often used for the voice coil of a high-end speaker.
Some of those coils are directly mounted on a printed circuit board depending on the applications. In such a case, with a coil used for a power supply circuit and so forth, there is the need for holding back the inductance of the coil, thereby causing a large current to flow through a narrow space, so that there have been many cases where the flat-type electric wire is used in those coils.
However, the flat-type electric wire, being a special item, has had a problem in that it lacks in marketability, is expensive, and its workability is poor. Furthermore, there has been available a method for concurrently winding two lengths of wires as bifilar winding, but this has had a problem of two lengths of wires getting entangled, requiring some special ideas.
There is proposed a multilayer coil, as a related prior art, for preventing wires from swelling in the direction of a core outer diameter in a face wherein the wire wires of an upper layer and those on the lower layer intersect by feeding the wires when two or more wire rods are wound in alignment on the core in parallel with each other (see, for example, patent document 1). However, this has a problem in that it needs a dedicated specific apparatus.    Patent Document: JP 2006-245298A